When used to colour plastics, it is important that a grade of Ultramarine pigment has consistent colour and dispersion properties. It must be low in unreacted sulphur so that odours are not released when it is heated to plastics processing temperatures and it must not contain excessively high moisture. For sensitive applications where regulatory approval is required, it must also have a low trace metal content. These properties are much less important in most other applications in which Ultramarine is used. It is normal for Ultramarine manufacturers to recommend a specific range of grades for use in colouring plastics in which these properties have been optimised.